In cellular networks, as a user equipment moves from cell to cell and performs cell selection/reselection and handover, the user equipment measures the signal strength/quality of neighboring cells. In a Long Term Evolution (LTE) network, for example, the user equipment measures two parameters of cell-specific reference signals (CRS)—RSRP (Reference Signal Received Power) and RSRQ (Reference Signal Received Quality).
The RSRP is the average received power of resource elements that carry CRS over a frequency bandwidth. Although RSRP is an important measure, on its own it provides no indication of signal quality. RSRQ provides this measure and is defined as the ratio of RSRP to the Received Signal Strength Indicator (RSSI). The RSSI parameter represents the received power for all subcarriers of the serving cell bandwidth, including the signal power, noise power, and interference power over all subcarriers. Accurate RSRP/RSRQ measurement can reduce the connection drop rate and therefore enhance user experience.
FIG. 3 illustrates a diagram of raw RSRP measurements reported from a user equipment's physical layer (L1 in the case of LTE) to a higher layer (L3 in the case of LTE), as is known. The physical layer performs raw RSRP measurements several times and then reports the measurements to the higher layer with a maximum period of 200 ms for intra-frequency measurement and 480 ms for inter-frequency measurement.
In a Radio Resource Control (RRC) connected state, the reported RSRP is time filtered in the higher layer to smooth the measurement results. The period that the physical layer reports the measurement results to the higher layer filter is relatively long. As a result, the reported measurement results may not accurately reflect the RSRP at the time stamp of reporting.